1. Department of Molecular Microbiology, Washington University Medical Center, St. Louis, MO 63110.
2. Department of Cell Biology and Physiology, Washington University Medical Center, St. Louis, MO 63110.
3. Department of Microbiology, University of Hawaii, Honolulu, HI 96822.
4. Department of Medicine, Washington University Medical Center, St. Louis, MO 63110.